This invention relates to a hydraulic pressure control device which permits intervention of electronic control in vehicle braking without changing over a hydraulic circuit, and a vehicle brake device using it.
Among known vehicle brake devices which permit intervention of electronic control, there is a brake-by-wire type device.
This type of brake device has a circuit configuration as shown in FIG. 9 (which shows only a circuit in one line). When a brake pedal 51 is depressed, a fluid line 54 extending from a master cylinder 52 to wheel brakes 53 is shut off by a changeover valve 55. Brake fluid pressure is supplied from a hydraulic pressure source 56 provided with a power-driven pump through a hydraulic pressure control valve 57 and a changeover valve 58 to the wheel brakes 53. The hydraulic pressure control valve 57 uses a spool valve to adjust the brake hydraulic pressure from the hydraulic pressure source 56 to a value proportional to the exciting current and outputs it. In the figure, 59 is a reservoir. This type of control valve is known as one which permits delicate hydraulic pressure control compared with hydraulic pressure control valves in which a pressure increasing valve and a pressure reducing valve are combined. A brake-by-wire type brake device using such a control valve is disclosed e.g. in JP patent publication 2757862.
A vehicle brake device of a brake-by-wire type is high in freedom of intervention of electronic control. Besides braking based on the intent of the driver, it can perform various controls such as BA (brake-assist) control, automatic braking such as ASC (active stability control) which, while the driver is not operating the brake pedal, an ECU (electronic control device) 60 performs judging the necessity of speed decrease and vehicle position control, and regenerative blending brake control for electric vehicles and hybrid cars.
In such a conventional vehicle brake device, upon depressing of the brake pedal 51, it is detected by a brake switch to close the changeover valve 55, and brake hydraulic pressure from the hydraulic pressure source 56, which is in a separate line, is controlled to a value corresponding to a command from the ECU 60 by means of the hydraulic pressure control valve 57 and supplied to the wheel brakes.
Also, a failure in the line connecting to the hydraulic pressure source 56 is detected based on sensor information from e.g. pressure sensors 61a and 61b. When a failure occurs, the changeover valve 55 is opened to supply the brake fluid pressurized in the master cylinder 52 to the wheel brakes 53.
Such a conventional device in which detection of a failure is done based on sensor information is inferior in reliability. If the information from sensors is wrong, it is possible that control based on wrong information is carried out, so that even if the line connecting with the hydraulic pressure source 56 fails, the changeover valve 55 is not opened and the brakes do not work.
Also, sensors for detecting a failure and circuits for carrying out failure judgment are needed. This increases the cost.
An object of this invention is to provide a simple and highly reliable hydraulic pressure control device and a vehicle brake device using the same.
According to this invention, there is provided a hydraulic pressure control device comprising a housing formed with an input port connected to a hydraulic pressure source, an output port connected to wheel brakes, and a discharge port, a spool valve mounted in the housing so as to be acted by a brake operating force, a first valve portion formed between the spool valve and the discharge port so as to close to disconnect the output port from the discharge port when the spool valve advances, and when the spool valve further makes advancing displacement, a second valve portion formed between the spool valve and the input port so as to open when the spool valve advances further, whereby bringing the input port into communication with the output port, the degrees of opening of the respective valve portions being adjusted according to the amount of displacement of the spool valve, whereby outputting a hydraulic pressure balancing with the brake operating force acted on the spool valve, an offset spring for biasing the spool valve in a backward direction to impart an offset force corresponding to the amount of pressure reduction required for pressure-reducing control, and a pressure chamber for applying hydraulic pressure introduced from outside to the spool valve in an advancing direction.
Also, there is provided a vehicle brake device comprising the hydraulic pressure control device claimed in claim 1, a hydraulic pressure source connected to the input port of the hydraulic pressure control device, a reservoir, a pressure-adjusting valve for receiving a substantially constant pressure P1 from the hydraulic pressure source and supplying it to the pressure chamber, a first valve for pressure increase control for opening and closing a fluid passage connecting between the pressure-adjusting valve and the pressure chamber, and a valve for pressure reduction control for opening and closing a fluid passage connecting between the pressure chamber and the reservoir, wherein the area a of a pressure-receiving portion of the spool valve which faces the pressure chamber, the force F of the offset spring, and the pressure P1 adjusted by the pressure-adjusting valve are set so as to satisfy the formula axc2x7P1 less than F.
Further, there is also provided a vehicle brake device wherein a fluid passage extending from the hydraulic pressure source to the pressure chamber of the hydraulic pressure control device is provided, and a second valve for pressure increase control is provided in the fluid passage for BA control and automatic braking.
In these vehicle brake devices, it is preferable that at least one of the first valve for pressure increase control and the valve for pressure reduction control is a valve capable of electric pressure control. Also, a relief valve is preferably provided between the pressure-adjusting valve and the first valve for pressure increase control.
Further, according to this invention, there is also provided a vehicle brake device wherein the wheel brakes are divided into two lines, namely, a first line and a second line, with the wheel brakes in the first line in communication with the output port of the hydraulic pressure control device, further comprising a master cylinder and a copying valve, the master cylinder comprising a first piston acted by a brake operating force, a second piston arranged in front of the first piston, a spring arranged between the first piston and the second piston, brake fluid between the first piston and the second piston being pressurized, the master cylinder transmitting the brake operating force to the spool valve of the hydraulic pressure control device through the first piston, the spring and the second piston, the copying valve closing under fluid pressure in the first line while the first line is normal, to shut off a fluid passage extending from the master cylinder to the wheel brakes in the second line, whereby transmitting the hydraulic pressure in the first line to the wheel brakes in the second line, and if the first line fails, the copying valve being kept open so that brake fluid pressurized by the master cylinder is supplied to the wheel brakes in the second line.
In the vehicle brake device according to this invention, during normal braking, since the pressure chamber of the hydraulic pressure control device of this invention is maintained at hydraulic pressure P1 adjusted by the pressure-adjusting valve and the pressure P1 balances with the offset spring force F, when an operating force is applied from a brake operating member such as the brake pedal to the spool valve, the hydraulic pressure control device, which has the spool valve, adjusts the hydraulic pressure supplied from the hydraulic pressure source to a value corresponding to the brake operating force (which is larger than the hydraulic pressure that can be generated manually) and outputs it. Thus, during normal braking, braking is done based on the will of the driver.
During pressure reduction control such as regenerative blending brake control, the driver applies an operating force to the spool valve in the same manner as during normal braking. But at this time, the first valve for pressure increase control and the valve for pressure reduction control are driven on command from the ECU to lower the hydraulic pressure introduced into the pressure chamber in the range of P1 to 0, thereby weaking the braking force.
Further, during pressure increase control such as automatic braking, the second valve for pressure increase control and the valve for pressure reduction control are driven on command from the ECU to control the hydraulic pressure in the pressure chamber in the range of P1 to Pmax (maximum hydraulic pressure that the hydraulic pressure source can generate). This hydraulic pressure applies force in the advancing direction to the spool valve, so that the brake hydraulic pressure from the hydraulic pressure source is adjusted to a value corresponding to the spool driving force which includes the input from the brake operating member and is supplied to the wheel brakes.
As described above, since pressure reduction and increase by electronic control are possible in addition to ordinary braking without changing over hydraulic circuits, it is not necessary to use failure judgement by the ECU for control. Even if the sensor information is wrong, the will of the driver is reliably reflected on braking, so that reliability of the device increases.
Operations and effects of the arrangements that have been described above as preferable will be described below.